Anti-apoptotic Bcl-2 family proteins are associated with a number of diseases and are under investigation as potential therapeutic drug targets. These targets for interventional therapy include, for example, the Bcl-2 family proteins Bcl-2, Bcl-XL and Bcl-w. Recently, inhibitors of Bcl-2 family proteins have been reported in commonly-owned PCT/US/2004/36770, published as WO 2005/049593 and PCT/US/2004/367911, published as WO 2005/049594. While this art teaches inhibitors having high binding to the target protein, compound binding affinity is only one of many parameters to be considered. One goal is to produce compounds that preferentially bind to, that is, are selective for, one protein over another protein. To exhibit this selectivity, it is well known that a compound not only displays a high binding affinity to a particular protein but a lower binding affinity for another member as well.
A typical measure of binding affinity of an anti-apoptotic protein inhibitor is the balance between the binding and dissociation processes between the protein and the inhibitor (Ki). The inhibition constant (Ki) is the dissociation constant of an enzyme-inhibitor complex or a protein/small molecule complex, wherein the small molecule is inhibiting binding of one protein to another protein. So a large Ki value indicates a low binding affinity, and a small Ki value indicates a high binding affinity.
A typical measure of cellular activity of an anti-apoptotic protein inhibitor is the concentration eliciting 50% cellular effect (EC50).
Accordingly, the inventors have discovered that while compounds taught in the art have utility for the treatment of various cancers and immune diseases, they are not selective for anti-apoptotic Bcl-2 proteins over anti-apoptotic Bcl-XL proteins and thereby result in a higher probability of side effects characterized by inhibition of anti-apoptotic Bcl-XL proteins such as, thrombocytopenia.
This invention therefore comprises a series of compounds that demonstrate unexpected properties with respect to their selectivity for binding to, and inhibiting the activity of anti-apoptotic Bcl-2 protein over anti-apoptotic Bcl-XL protein as significantly higher than those of the compounds taught in PCT/US/2004/36770 and PCT/US/2004/367911.